openldap: Make client binary install configurable

Some OpenLDAP deployment only need the client libraries and not the client
tools, so make the tool installation optional.

[Thomas: implement the for loop in make rather than in shell.]

Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>